The use of cable-drawn scrapers or scraping apparatus has also been suggested, in which one or more cables pull a wagon or sledge which holds the scraper at or near the bottom of the basin in a repeating to-and-fro motion. (SE-B-423 968; U.S. Pat. No. 2,866,557; U.S. Pat. No. 2,768,749; U.S. Pat. No. 4,090,966; GB-A-1 504 518). The technology is an improvement over the state of the art concerning chain-driven scrapers, in that it has a significantly simpler, lighter and cheaper construction. Meanwhile, the system means that different equipment must be used to turn the scraper blade and control its rotation from a vertical to a horizontal position and vice versa under the reciprocating movement caused by the cables. The scraper blade, which comprises a metal blade which is arranged with its edge in the transport direction and most often is provided with a rubber edging strip, extends across the width of the basin, at right angles to the direction of transport. Under the reciprocating movement of the scraper blade, the slurry is stirred up, however, to give so-called sludge escape, due to turbulence building up behind the blade and maximum efficiency cannot therefore be reached. The loads on the apparatus also mean that it must be made of metal, and to prevent corrosion from eating away the apparatus too quickly, it must be manufactured in a more acid-resistant material, which increases costs.
An apparatus in a sedimentation basin and the like for displacement of slurry and sediment collected on the bottom of the basin is known from SE-C-454,140, in which transport means is arranged to be moved back and forth near the bottom of the basin, whereby slurry and sediment is displaced by the reciprocating movement to one end of the basin, whereby the transporter consists of a mat comprising means with a wedge-shaped triangular cross-section, said means being arranged substantially perpendicular to the direction of travel of the transporter, and the point of the wedge is arranged in the return direction while the base of the wedge is arranged in the forward direction.
A transport element of a reciprocating scraper is also known from EP-B-O 532 484 for moving slurry in sedimentation basins and the similar objects in water purification plants, said element having a cross-section which has a downwardly-facing surface, a substantially curved convex surface and a substantially vertical concave surface, said concave surface being arranged in the forward, transporting direction.
All transport of slurry takes place with these elements placed in a perpendicular relationship to the longitudinal direction of the transporter, either a chain, net or rod move over the bottom of the sedimentation basin, whereby the chain moves continuously in one direction, and the net and rod move back and forth.
Previous transport elements have always been welded to longitudinally directed draw track, net and the similar on the top of these, which welding on one hand requires special training for the authorization of personal skilled in welding, and on the other hand creates tensions between the different materials, which leads to the fact that the transporting element bends and thereby carry out a less efficient transport. Often layers of sludge are built up underneath the transporting element, which sludge will not become transported but will become compressed and lifts the whole scraping transporter.